Electrochemical Cells are devices capable of either generating electrical energy from chemical reactions or facilitating chemical reactions through the introduction of electrical energy. An electrochemical cell consists of two half-cells. Each half-cell consists of an electrode and an electrolyte. The two half-cells may use the same electrolyte, or they may use different electrolytes. The chemical reactions in the cell may involve the electrolyte, the electrodes, or an external substance (as in fuel cells that may use hydrogen gas as a reactant). In a full electrochemical cell, species from one half-cell lose electrons (oxidation) to their electrode while species from the other half-cell gain electrons (reduction) from their electrode. Click here for more about redox reactions.
A Salt Bridge (e.g., filter paper soaked in KNO3, NaCl, or some other electrolyte) is often employed to provide ionic contact between two half-cells with different electrolytes, yet prevent the solutions from mixing and causing unwanted side reactions.
As electrons flow from one half-cell to the other through an external circuit, a difference in charge is established. If no ionic contact were provided, this charge difference would quickly prevent the further flow of electrons. A salt bridge allows the flow of negative or positive ions to maintain a steady-state charge distribution between the oxidation and reduction vessels, while keeping the contents otherwise separate.
Reduction potential is a measure of the tendency of a chemical species to acquire electrons and thereby be reduced. Reduction potential is measured in volts (V). Each species has its own intrinsic reduction potential; the more positive the potential, the greater the species' affinity for electrons and tendency to be reduced.
In aqueous solutions, reduction potential is a measure of the tendency of the solution to either gain or lose electrons when it is subject to change by introduction of a new species. A solution with a higher (more positive) reduction potential than the new species will have a tendency to gain electrons from the new species (i.e. to be reduced by oxidizing the new species) and a solution with a lower (more negative) reduction potential will have a tendency to lose electrons to the new species (i.e. to be oxidized by reducing the new species). Because the absolute potentials are difficult to accurately measure, reduction potentials are defined relative to a reference electrode. Reduction potentials of aqueous solutions are determined by measuring the potential difference between an inert sensing electrode in contact with the solution and a stable reference electrode connected to the solution by a salt bridge.
The standard reduction potential E0 is measured under standard conditions and metals in their pure state. The standard reduction potential is defined relative to a standard hydrogen electrode(SHE) reference electrode, which is arbitrarily given a potential of 0.00 volts.
Redox (short for reduction–oxidation reaction) is a chemical reaction in which the oxidation states of atoms are changed. Any such reaction involves both a reduction process and a complementary oxidation process, two key concepts involved with electron transfer processes.[1] Redox reactions include all chemical reactions in which atoms have their oxidation state changed; in general, redox reactions involve the transfer of electrons between chemical species. The chemical species from which the electron is stripped is said to have been oxidized, while the chemical species to which the electron is added is said to have been reduced. It can be explained in simple terms:
Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom, or ion.
Reduction is the gain of electrons or a decrease in oxidation state by a molecule, atom, or ion.
As an example, during the combustion of wood, oxygen from the air is reduced, transferring electrons from the carbon.[2] Although oxidation reactions are commonly associated with the formation of oxides from oxygen molecules, oxygen is not necessarily included in such reactions, as other chemical species can serve the same function.[2] The reaction can occur relatively slowly, as in the case of rust, or more quickly, as in the case of fire. There are simple redox processes, such as the oxidation of carbon to yield carbon dioxide (CO2) or the reduction of carbon by hydrogen to yield methane (CH4), and more complex processes such as the oxidation of glucose (C6H12O6) in the human body.
Electronics
Electrification is the process of powering by electricity and is usually associated with changing over from another power source. The broad meaning of the term, such as in the history of technology and economic history, usually applies to a region or national economy. Broadly speaking, electrification was the build out of the electrical generating and distribution systems which occurred in Britain, the United States, and other countries from the mid-1880s until around 1950 and is in progress in rural areas in some developing countries. This included the change over from line shaft and belt drive using steam engines and water power to electric motors.
Electrostatic charge-The electric charge at rest on the surface of an insulated body (which establishes an adjacent electrostatic field) Static charge- imbalance of electric charges within or on the surface of a material (separation of positive and negative charges)
Basic Law of Electrostatics- objects with similar charges repel each other; objects with opposite charges attract each other
Conductor- an object or type of material that allows the flow of an electrical current in one or more directions Ex: aluminum, gold, copper, silver Insulator- a substance that resists electricity Ex: rubber, wood, plastic, glass, air
where ke is Coulomb's constant (ke = 8.99×109 N m2 C−2), q1 and q2 are the signed magnitudes of the charges, and the scalar r is the distance between the charges. The force of interaction between the charges is attractive if the charges have opposite signs (i.e. F is negative) and repulsive if like-signed (i.e. F is positive).
An electric field is a vector field that associates to each point in space the Coulomb force that would be experienced per unit of electric charge, by an infinitesimal test charge at that point.[1] Electric fields converge and diverge at electric charges and can be induced by time-varying magnetic fields. The electric field combines with the magnetic field to form the electromagnetic field.
An electric line of force is an imaginary continuous line or curve drawn in an electric field such that tangent to it at any point gives the direction of the electric force at that point.The direction of a line of force is the direction along which a small free positive charge will move along the line.
Electric Potential
V=Work(W)/charge(q) An electric potential (also called the electric field potential or the electrostatic potential) is the amount of electric potential energy that a unitary point electric charge would have if located at any point in space, and is equal to the work done by an external agent in carrying a unit of positive charge from the arbitrarily chosen reference point (usually infinity) to that point without any acceleration.
A capacitor is a passivetwo-terminalelectrical component that stores electrical energy in an electric field.[1] The effect of a capacitor is known as capacitance. While capacitance exists between any two electrical conductors of a circuit in sufficiently close proximity, a capacitor is specifically designed to provide and enhance this effect for a variety of practical applications by consideration of size, shape, and positioning of closely spaced conductors, and the intervening dielectric material. A capacitor was therefore historically first known as an electric condenser.[2]
C=Q/V
C=capacitance
Q=quantity of charge
V=the potential difference between the conducting plates
Dielectric material A dielectric material (dielectric for short) is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material as they do in a conductor, but only slightly shift from their average equilibrium positions causing dielectric polarization.
Dielectric constant = K K=C2/C1
Combination of Capacitors -For capacitors connected in parallel...
- CT=C1 + C2 + C3....
-For capacitors connected in series...
- 1/CT= 1/C1 + 1/C2 + 1/C3... Direct Current Circuits
Current
Current (I) = charge(Q)/ time (t)
Unit of current is the ampere (A)
One ampere is a current of 1 coulomb per second
Resistance The electrical resistance of an electrical conductor is a measure of the difficulty to pass an electric current through that conductor. The inverse quantity is electrical conductance, and is the ease with which an electric current passes. Electrical resistance shares some conceptual parallels with the notion of mechanical friction. The SI unit of electrical resistance is the ohm (Ω), while electrical conductance is measured in siemens (S).
An electrical circuit is a network consisting of a closed loop, giving a return path for the current. Linear electrical networks, a special type consisting only of sources (voltage or current), linear lumped elements (resistors, capacitors, inductors), and linear distributed elements (transmission lines), have the property that signals are linearly superimposable. They are thus more easily analyzed, using powerful frequency domain methods such as Laplace transforms, to determine DC response, AC response, and transient response.
Sources of continuous current
electromagnetic
photoelectric
thermoelectric
piezoelectric
chemical
Faradays Experiment
1. All the static charge on a conductor lies on its surface.
2. There can be no potential difference between two points on the surface of a charged conductor
3. The surface of a conductor is an equipotential surface.
4. Electric lines of force are normal to equipotential surfaces.
5. Lines of force originate or terminate normal to the conductive surface of a charged object.
Combinations of cells
-IF the cells are connected in series..
-the emf* of the battery is equal to the sum of the emfs of the individual cells
- The current in each cell and in the external circuit has the same magnitude throughout
- The internal resistances of the battery is equal to the sum of the internal resistances of the individual cells
The emf (electromotive force) of a source is the energy per unit charge supplied by the source, measured in volts.
-If cells are connected in parallel.. -the emf is equal to the emf of each separate cell - the total current in the circuit is divided equally among the cells - the reciprocal of the internal resistance of the batter is equal to the sum of the reciprocals of the internal resistances of the cells
Ohm's Law Ohm's law** states that the current through a conductor between two points is directly proportional to the voltage across the two points. Introducing the constant of proportionality, the resistance,[1] one arrives at the usual mathematical equation that describes this relationship:[2]
-The constant is the resistant of the circuit
V=IR
P=IV
P=I2R
Laws of Resistance
The resistance of all substances changes with temperature
The resistance of a uniform conductor is directly proportional to the length of the conductor
The resistance of a uniform conductor is inversely proportional to its cross-sectional area
The resistance of a given conductor depends on the material of which it is made
Wikipedia contributors. "Electrochemical cell." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 14 Dec. 2016. Web. 14 Dec. 2016.
Wikipedia contributors. "Reduction potential." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 14 Dec. 2016. Web. 14 Dec. 2016.
Wikipedia contributors. "Redox." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 5 Jan. 2017. Web. 5 Jan. 2017.
Electrochemistry
Table of Contents
Electrochemical Cells
Electrochemical Cells are devices capable of either generating electrical energy from chemical reactions or facilitating chemical reactions through the introduction of electrical energy.
An electrochemical cell consists of two half-cells. Each half-cell consists of an electrode and an electrolyte. The two half-cells may use the same electrolyte, or they may use different electrolytes. The chemical reactions in the cell may involve the electrolyte, the electrodes, or an external substance (as in fuel cells that may use hydrogen gas as a reactant). In a full electrochemical cell, species from one half-cell lose electrons (oxidation) to their electrode while species from the other half-cell gain electrons (reduction) from their electrode. Click here for more about redox reactions.
A Salt Bridge (e.g., filter paper soaked in KNO3, NaCl, or some other electrolyte) is often employed to provide ionic contact between two half-cells with different electrolytes, yet prevent the solutions from mixing and causing unwanted side reactions.
As electrons flow from one half-cell to the other through an external circuit, a difference in charge is established. If no ionic contact were provided, this charge difference would quickly prevent the further flow of electrons. A salt bridge allows the flow of negative or positive ions to maintain a steady-state charge distribution between the oxidation and reduction vessels, while keeping the contents otherwise separate.
Reduction Potential
Reduction potential is a measure of the tendency of a chemical species to acquire electrons and thereby be reduced. Reduction potential is measured in volts (V). Each species has its own intrinsic reduction potential; the more positive the potential, the greater the species' affinity for electrons and tendency to be reduced.
In aqueous solutions, reduction potential is a measure of the tendency of the solution to either gain or lose electrons when it is subject to change by introduction of a new species. A solution with a higher (more positive) reduction potential than the new species will have a tendency to gain electrons from the new species (i.e. to be reduced by oxidizing the new species) and a solution with a lower (more negative) reduction potential will have a tendency to lose electrons to the new species (i.e. to be oxidized by reducing the new species). Because the absolute potentials are difficult to accurately measure, reduction potentials are defined relative to a reference electrode. Reduction potentials of aqueous solutions are determined by measuring the potential difference between an inert sensing electrode in contact with the solution and a stable reference electrode connected to the solution by a salt bridge.
The standard reduction potential E0 is measured under standard conditions and metals in their pure state. The standard reduction potential is defined relative to a standard hydrogen electrode(SHE) reference electrode, which is arbitrarily given a potential of 0.00 volts.
Calculating Reduction Potential
https://www.chem.wisc.edu/deptfiles/genchem/netorial/rottosen/tutorial/modules/electrochemistry/05potential/18_52.htmRedox Reactions
Redox (short for reduction–oxidation reaction) is a chemical reaction in which the oxidation states of atoms are changed. Any such reaction involves both a reduction process and a complementary oxidation process, two key concepts involved with electron transfer processes.[1] Redox reactions include all chemical reactions in which atoms have their oxidation state changed; in general, redox reactions involve the transfer of electrons between chemical species. The chemical species from which the electron is stripped is said to have been oxidized, while the chemical species to which the electron is added is said to have been reduced. It can be explained in simple terms:
- Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom, or ion.
- Reduction is the gain of electrons or a decrease in oxidation state by a molecule, atom, or ion.
As an example, during the combustion of wood, oxygen from the air is reduced, transferring electrons from the carbon.[2] Although oxidation reactions are commonly associated with the formation of oxides from oxygen molecules, oxygen is not necessarily included in such reactions, as other chemical species can serve the same function.[2]The reaction can occur relatively slowly, as in the case of rust, or more quickly, as in the case of fire. There are simple redox processes, such as the oxidation of carbon to yield carbon dioxide (CO2) or the reduction of carbon by hydrogen to yield methane (CH4), and more complex processes such as the oxidation of glucose (C6H12O6) in the human body.
Electronics
Electrification is the process of powering by electricity and is usually associated with changing over from another power source. The broad meaning of the term, such as in the history of technology and economic history, usually applies to a region or national economy. Broadly speaking, electrification was the build out of the electrical generating and distribution systems which occurred in Britain, the United States, and other countries from the mid-1880s until around 1950 and is in progress in rural areas in some developing countries. This included the change over from line shaft and belt drive using steam engines and water power to electric motors.
Electrostatic charge-The electric charge at rest on the surface of an insulated body (which establishes an adjacent electrostatic field)
Static charge- imbalance of electric charges within or on the surface of a material (separation of positive and negative charges)
Basic Law of Electrostatics- objects with similar charges repel each other; objects with opposite charges attract each other
Conductor- an object or type of material that allows the flow of an electrical current in one or more directions
Ex: aluminum, gold, copper, silver
Insulator- a substance that resists electricity
Ex: rubber, wood, plastic, glass, air
Coulomb's law or Coulomb's inverse-square law, is a law of physics that describes force interacting between static electrically chargedparticles. In its scalar form the law is:
where ke is Coulomb's constant (ke = 8.99×109 N m2 C−2), q1 and q2 are the signed magnitudes of the charges, and the scalar r is the distance between the charges. The force of interaction between the charges is attractive if the charges have opposite signs (i.e. F is negative) and repulsive if like-signed (i.e. F is positive).
Who, what, when?
The law was first published in 1784 by French physicist Charles Augustin de Coulomb and was essential to the development of the theory of electromagnetism. It is analogous to Isaac Newton's inverse-square law of universal gravitation. Coulomb's law can be used to derive Gauss's law, and vice versa. The law has been tested extensively, and all observations have upheld the law's principle.
K= 8.987 X 109 vacuum
8.93 X 109 in air
An electric field is a vector field that associates to each point in space the Coulomb force that would be experienced per unit of electric charge, by an infinitesimal test charge at that point.[1] Electric fields converge and diverge at electric charges and can be induced by time-varying magnetic fields. The electric field combines with the magnetic field to form the electromagnetic field.
An electric line of force is an imaginary continuous line or curve drawn in an electric field such that tangent to it at any point gives the direction of the electric force at that point.The direction of a line of force is the direction along which a small free positive charge will move along the line.
Electric Potential
V=Work(W)/charge(q)
An electric potential (also called the electric field potential or the electrostatic potential) is the amount of electric potential energy that a unitary point electric charge would have if located at any point in space, and is equal to the work done by an external agent in carrying a unit of positive charge from the arbitrarily chosen reference point (usually infinity) to that point without any acceleration.
A capacitor is a passive two-terminal electrical component that stores electrical energy in an electric field.[1] The effect of a capacitor is known as capacitance. While capacitance exists between any two electrical conductors of a circuit in sufficiently close proximity, a capacitor is specifically designed to provide and enhance this effect for a variety of practical applications by consideration of size, shape, and positioning of closely spaced conductors, and the intervening dielectric material. A capacitor was therefore historically first known as an electric condenser.[2]
C=Q/V
C=capacitance
Q=quantity of charge
V=the potential difference between the conducting plates
Dielectric material
A dielectric material (dielectric for short) is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material as they do in a conductor, but only slightly shift from their average equilibrium positions causing dielectric polarization.
Dielectric constant = K
K=C2/C1
Combination of Capacitors
-For capacitors connected in parallel...
- CT=C1 + C2 + C3....
-For capacitors connected in series...
- 1/CT= 1/C1 + 1/C2 + 1/C3...
Direct Current Circuits
Resistance
The electrical resistance of an electrical conductor is a measure of the difficulty to pass an electric current through that conductor. The inverse quantity is electrical conductance, and is the ease with which an electric current passes. Electrical resistance shares some conceptual parallels with the notion of mechanical friction. The SI unit of electrical resistance is the ohm (Ω), while electrical conductance is measured in siemens (S).
An electrical circuit is a network consisting of a closed loop, giving a return path for the current. Linear electrical networks, a special type consisting only of sources (voltage or current), linear lumped elements (resistors, capacitors, inductors), and linear distributed elements (transmission lines), have the property that signals are linearly superimposable. They are thus more easily analyzed, using powerful frequency domain methods such as Laplace transforms, to determine DC response, AC response, and transient response.
Sources of continuous current
Faradays Experiment
1. All the static charge on a conductor lies on its surface.
2. There can be no potential difference between two points on the surface of a charged conductor
3. The surface of a conductor is an equipotential surface.
4. Electric lines of force are normal to equipotential surfaces.
5. Lines of force originate or terminate normal to the conductive surface of a charged object.
Combinations of cells
-IF the cells are connected in series..
-the emf* of the battery is equal to the sum of the emfs of the individual cells
- The current in each cell and in the external circuit has the same magnitude throughout
- The internal resistances of the battery is equal to the sum of the internal resistances of the individual cells
-If cells are connected in parallel..
-the emf is equal to the emf of each separate cell
- the total current in the circuit is divided equally among the cells
- the reciprocal of the internal resistance of the batter is equal to the sum of the reciprocals of the internal resistances of the cells
Ohm's Law
Ohm's law** states that the current through a conductor between two points is directly proportional to the voltage across the two points. Introducing the constant of proportionality, the resistance,[1] one arrives at the usual mathematical equation that describes this relationship:[2]
-The constant is the resistant of the circuit
Laws of Resistance
Wikipedia contributors. "Electrochemical cell." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 14 Dec. 2016. Web. 14 Dec. 2016.
Wikipedia contributors. "Reduction potential." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 14 Dec. 2016. Web. 14 Dec. 2016.
Wikipedia contributors. "Redox." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 5 Jan. 2017. Web. 5 Jan. 2017.
Wikipedia contributors. "Electrification." Wikipedia. Wikimedia Foundation, n.d. Web. 18 Jan. 2017.
Wikipedia contributors. "Coulomb's Law." Wikipedia. Wikimedia Foundation, n.d. Web. 18 Jan. 2017.
Wikipedia contributors. "Electric Field." Wikipedia. Wikimedia Foundation, n.d. Web. 18 Jan. 2017.
Wikipedia contributors. "Electric Potential." Wikipedia. Wikimedia Foundation, n.d. Web. 18 Jan. 2017.
Wikipedia contributors. "Capacitor." Wikipedia. Wikimedia Foundation, n.d. Web. 18 Jan. 2017.
Wikipedia contributors. "Dielectric." Wikipedia. Wikimedia Foundation, n.d. Web. 18 Jan. 2017.
Wikipedia contributors. "Electrical Resistance and Conductance." Wikipedia. Wikimedia Foundation, n.d. Web. 18 Jan. 2017.
Wikipedia contributors. "Electrical Network." Wikipedia. Wikimedia Foundation, n.d. Web. 18 Jan. 2017.
Wikipedia contributors. "Ohm's Law." Wikipedia. Wikimedia Foundation, n.d. Web. 18 Jan. 2017.